This invention relates to rivetless chains such as used in overhead trolley conveyors, and particularly to reconditioning worn links of chains by applying concentrated heat and pressure longitudinally to the links.
Overhead trolley conveyors are commonly used in manufacturing assembly lines. Plants for assembling automobiles and farm machinery use such conveyors extensively to carry heavy components and heavy assemblies. The loads are supported on carriers that are suspended from brackets that pass upwardly through center links of chains to trolley wheels supported by overhead track. The center links have the shape of closed, elongated loops and are alternate links of continuous chains that are driven by sprockets or by caterpillar drives to move the loads. The links between the center links are pairs of parallel side links. The adjacent ends of each pair of side links overlap a relatively large end of a center link, and a pin having a T-head at each end has a shank extending through the ends of the side links and through the intermediate end of the central link. The ends of the center links have greater heights than their intermediate portions to facilitate assembly and disassembly and to increase load-bearing surfaces tending to wear.
Driven sprockets enter the chains between pairs of side links and apply successively to one end of each center link a longitudinal force to run the conveyors. The changes in direction of the movement of the chains of the conveyors as required to move loads to different lines of assembly are provided by wheel turns along the tracks. While the chains are guided around wheels, the center links pivot about the pins, the pins being restrained from rotation in the side links by the T-heads within slots in the ends of the side links. The inside surfaces of the ends of the center links and the contiguous portions of the shanks of the pins wear whenever conveyors are operating, and wear is most likely at the turns of the conveyors.
When the chains wear to such an extent that their respective lengths increase more than about three percent, the operation of the chains is impaired because spacings between successive pairs of side links are longer than the distance between successive driving sprockets. Since chains can be reconditioned at small cost compared with the cost of new chains, the chains may be reconditioned and placed back into service. The usual method of reconditioning worn chains comprises disassembling and cleaning the links and replacing pins. Although the replacement of the pins or their rotation through 180 degrees after the chains are first worn decreases the length of the chains sufficiently to restore them for satisfactory and limited extended use, the expensive center links with continued use become worn to such an extent that they must be replaced after the pitch of the worn links no longer match the pitch of the driving sprockets.